Process for the continuous preparation of unsaturated polyesters

ABSTRACT

Process for the continuous preparation of unsaturated polyesters, comprising bringing olefinically unsaturated dicarboxylic acids or their anhydrides, if desired, together with saturated dicarboxylic acids of their anhydrides (dicarboxylic acid component) and dihydric alcohols, if desired, together with higher polyhydric alcohols (alcohol component) into contact in molar ratios of from about 1.5:1 to 1.95:1 in a first reaction phase, operating at a temperature of from about 100* to 160*C and with residence times of from about 5 to 40 minutes to cause the formation of a corresponding half-ester; adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in the range of from about 0.87:1 to 0.97:1; bringing about the polyesterification in a second reaction phase by treating the product obtained in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure, for times of about 2 to 8 hours, and at temperatures of from about 100* to 220*C, the temperature in said stages not differing by more than about 10*C, and the water formed during the polyesterification being eliminated from each of the said stages; evaporating the residual water and the excess of the alcohol component from the polyesterification product obtained with operation at pressures below atmospheric pressure.

United States Patent 11 1 Vargiu et al.

l l PROCESS FOR THE CONTINUOUS PREPARATION OF UNSATURATED POLYESTERS [75] Inventors: Silvio Vargiu, Sesto S. (iimanni (Milan I; Beppino Passalenti; Ugo Nistri, both of Milan all of Italy [73] Assignee: Societa Italiani Resine SIR. S.p.A.,

Milan, Italy [22] Filed: Nov. 29, 1973 [2]] Appl. No: 420,348

[] Foreign Application Priority Data Nov. 30 I972 ltaly.. 32278/72 [52] US. Cl 260/861; 260/75 M; 260/75 UA [51} Int. Cl. C08G 63/22; C08G 65/52 [58] Field of Search 260/ M, 75 UA. 861

[56] References Cited UNITED STATES PATENTS 3,252.94l 5/l966 Mayer et al i 260/75 OTHER PUBLICATIONS KirkOthmer Encyclopedia of Chemical Technology. 2nd Ed; V. 20, 800 I968].

Fri/liar Examiner-Howard E. Schain Asxixltm! EXGIHI Hr'r W. C. Danison, Jr.

Anoma y, Agent, or Firm--Sughrue. Rothwell, Mion, Zinn & Macpeak 1 Oct.7,l975

[57] ABSTRACT Process for the continuous preparation of unsaturated polyesters. comprising bringing olefinically unsaturated dicarboxylic acids or their anhydrides, if desired. together with saturated dicarboxylic acids of their anhydrides (dicarboxylic acid component) and dihydric alcohols, if desired, together with higher polyhydric alcohols (alcohol component) into contact in molar ratios of from about 15:1 to 1.95:1 in a first reaction phase, operating at a temperature of from about to C and with residence times of from about 5 to 40 minutes to cause the formation of a corresponding half-ester; adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in the range of from about 0.87:] to 0.97:1; bringing about the polyesterification in a second reaction phase by treating the product obtained in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmo spheres to atmospheric pressure, for times of about 2 to 8 hours and at temperatures of from about IUU to 220C. the temperature in said stages not differing by more than about 10C and the water formed during the polyesterification being eliminated from each of the said stages; evaporating the residual water and the excess of the alcohol component from the polyesterification product obtained with operation at pressures below atmospheric pressure.

PROCESS FOR THE CONTINL'OLS PREPARATION OF LNSATL'RA'IED POLYESTERS BACKGROUND OF THE 1. Field of the lnvention The present invention relates to a continuous process for the preparation of unsaturated polyesters.

Unsaturated polyesters are a class of soluble. essentially linear. low molecular weight macromolecules which contain both carboxylic ester groups and carbon-carbon double bonds as recurring units along the main chain. These unsaturated polyesters are usually prepared by condensation of (a) ethylcnically unsatu rated dicarboxylic acids or their anhydrides to impart the unsaturation. (b) saturated dicarboxylic acids or their anhydrides to modify the unsaturated polyesters and (c) dihydric alcohols. Unsaturated polyesters are diluted to liquid mixtures with reactive diluents such as styrene. methyl methacrylate or other polymerizable monomeric acrylic or vinyl compounds. These liquid mixtures are hereinafter termed as unsaturated polyester resins. 'l'hese mixtures can be cured in the presence of poIynieri/ation initiators to produce erosslinked strong solids. Both in the manufacture and use of unsaturated polyesters it is necessary that the formulation contain free radical inhibitors; cf. Kirk-Othmer. Encyclopedia of Chemical Technology. Second Edition. Vol. 10 t 1969}. pp. 79l to 839 and Encyclopedia of Polymer Science and Technology. \"ol. 1 l 1969), pp. 129 to ms.

2. Description of the Prior Art In normal practice. in the batchwise preparation of unsaturated polyesters the reactants comprising the ethy lenically unsaturated dicarboxylic acid or its anhydride. a saturated dicarboxylic acid or its anhydride and a dihydrie alcohol are heated for about 6 to 20 hours to temperatures of from about 180 to 230C For the removal of water formed during the estcrification the mixture is sparged with an inert gas. It is also possible to add to the mixture a solvent such as Xylene which together with the formed water forms an azeotropic mixture which is distilled off. This measure is. however. seldom used in practice since it causes additional costs and difficulties in removing the last traces of solvent from the unsaturated polyester.

Apart from the long reaction time the discontinuous operation has the disadvantage that one almost never obtains complete rcpreducibility of the results and hence absolute constancy of the characteristics of the products.

A need was therefore felt for the manufacture of unsaturated polyesters by a continuous operation which gives reproducible results. A continuous process nor mally gives a higher yield per time unit and per unit of the et'fectiv e volume of the reactor. a greater possibility of automation ot the plant. and a greater constancy of the characteristics of the product than a discontinuous process.

In principle. the manufacture of unsaturated polyesters can be carried out in a continuous operation by feeding the reactants to the one end of a reaction zone having an elongated. cg. tubular shape and being maintained at elevated temperature. ln this reaction zone the residence time of the reactants is controlled so that the reaction is carried to completion. The products are discharged at the other end of the reaction zone. It is found in practice that the conventional continuous processes have various disadvantages. For example. no suitable means have been found for the immediate removal of the water formed during esterification. It is well known that water is undesirable in an esterification reaction. since it tends to cause the reverse reaction to the esterifcation and so acts in practice as an inhibitor of the reaction.

Moreover. it has not so far been possible to prepare unsaturated polyesters by continuous operation with the use of conventional techniques and equipment. When the reacting mass is maintained by the normal means of heat exchange at the high temperatures required in the phase in which the completion of the reaction occurs and for the times required for this completion. gelation in the mass and progressive deposition of the gelled mass inside the reactor may occur. These deposited materials can be removed only by stopping the equipment and washing with solvents or scraping. On the other hand, if the deposits are allowed to accumulate. the efficiency of the heat exchange progressively decreases and the effective volume of the e uipment is also reduced.

It is though that one reason for the lack of success in the preparation of unsaturated polyesters by a continuous process lies in the fact that the temperature was raised as the polyesterification reaction proceeded in the same way as in discontinuous execution.

SUMMARY One object ofthe invention is to provide a simple and com enicnt process for the continuous preparation of unsaturated polyesters. vvhcrcin the water thus formed is removed immediately and no deposits are formed in the reaction zone. Further objects will be apparent from the following description.

[be invention consists essentially in carrying out the polyesteriiication reaction by continuous operation via several reaction stages in series with one another, in which the same temperature or approximately the same temperature is maintained. a pressure that progressively decreases from values of a few atmospheres to atmospheric pressure being maintained in these stages.

Moreover. elimination of the polyestcrification \vatcr occurs in each ofthe said stages. the elimination taking place under the particular conditions of temperature and pressure used.

More particularly. according to the process of the present invention:

The formation of a half-estcr is carried out in a first reaction phase by reaction of an ethylenically unsaturated dicarboxylic acid or its anhydride and a sattr rated dicarboxylic acid or its anhy dride with a quan tity of a dihydric alcohol smaller than that theoreti cally necessary for the formation of the unsaturated polyester.

A further quantity of dihydric alcohol is added to the hall ester obtained in this way and the mixture is subjected to polyesterilication in a second reaction phase via several stages maintained at the same temperature or approximately the same temperature and at a pressure decreasing from a few atmospheres to atmospheric pressure The number of the said stages is at least two. and elimination of polyesteritication Water occurs in each of these.

The residual water and any excess of the dihydric aleoho] are then eliminated from the polyesteritication product obtained in this way. the operation being carried out at a pressure below atmospheric pressure by a rapid distillation technique.

According to a preferred embodiment of the process ofthe present invention unsaturated polyesters are prepared by a. bringing olefinically unsaturated dicarboxylic acids or their anhydrides. if desired. together with saturated dicarboxylic acids or their anhydrides (dicarboxylic acid component) and dihydric alcohols. if desired. together with higher polyhydric alcohols (alco hol component) into contact in molar ratios of from about l.5:l to [.9521 in a first reaction phase. operating at a temperature of from about ltll) to l6UC and with residence times of from about 5 to 40 minutes to cause the formation of a corresponding half-ester; adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in the range of from about ().l's7:l to 0.97: l; cv bringing about the polyesterifcation in a second reaction phase by treating the product obtained in b) in at least two separate and successive stages. which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure. for times of from about 2 to ti hours. and at temperatures of from about ltltl to 210C. the temperature in said stages not differing by more than about l()(. the water formed during the polyesterification being eliminated from each of the said stages:

d. evaporating the residual water and the excess of the alcohol component from the polyesterilication product obtained in c) with operation at pressures below atmospheric pressure.

In the specification and claims the dicarboxylic acid component denotes the cthylenically unsaturated dicarboxylic acid and/or its anhydride which contains. if desired. a saturated dicarbovylic acid and/or its anhy dride and the term alcohol component denotes the dihydric alcohol which contains. if desired. a higher polyhydric alcohol.

In the attached PK}. 1. the reference I denotes the reactor in which the formation of the halt ester occurs. The ethylenically unsaturated dicarboxylic acid or its anhydride. if desired. together with a saturated dicar boxylic acid or its anhydride (dicarboxylic acid compo nent) is fed continuously into reactor 1. which is fitted with a stirrer. through the pipe 7.

The dihydric alcohol. if desired. together with a higher polyhydric alcohol [alcohol component) is fed through the pipe 8 and partly introduced into reactor 1 throught the pipe 9. the remainder being fed to reac tor 2 throught the pipe 10. In particular. the conditions are adjusted in such a way as to ensure in the reactor 1 a molar ratio of the dicarboxylic acid component to the alcohol component of about l.5:l to 1.95: l More over. a temperature of from about ltlU to lbU C is maintained in the reactor l. with a residence time of from about 5 to 4t) minutes. During the formation of the half-ester. one normally operates at atmospheric pressure and no elimination of any component from the reaction space occurs.

lhe halt ester is discharged from the reactor 1 through the pipe II and is mixed with a further quantity of the alcohol component in such a way as to en sure a molar ratio of the dicarboxylic acid component 5 to the alcohol component of about tl.87:l to (3.97:1.

According to the process of the present invention. the polyesteritication phase is carried out via several reaction stages. ln particular. the number ofsuch stages should be at least 2. and may have high values. eg. up to H). In practice. however. it has been found that it is convenient to use 3 or 4 reaction stages.

According to an essential aspect of the present invention. the polyesterification is carried out by operating at pressures that progressively decrease in the various stages from a value of a few atmospheres to atmospheric pressure. The pressure can thus vary from about 5 atmospheres in the first stage to l atmosphere in the last stage. It has been found in practice that it is preferably to operate at maximum pressure values of about 3 to 4 atmospheres According to another essential aspect of the process of the present invention. the same temperature or approximately the same temperature is maintained in each stage of the polyesterification. this temperature 35 possibly having values in the range of from about ltlt)" to 320C. In practice. when it is stated that the same temperature or approximately the same temperature is maintained. it is meant that the difference between the maximum value and the minimum value of the temper ature in the various stages of the polyesteritication does not exceed about 10C,

Moreover. according to the process ofthe present invention. the water formed in the polyesteril'ication is eliminated from each individual stage of the second re action phase under the conditions of temperature and pressure used. The total residence time of the mixture ofthe reactants under the polyesteritication conditions is chosen in such a way as to reach a conversion degree of the reactants of about (1,8(lzl to ().85:l. where the conversion degree means the molar ratio of the dicar boxylic acid component that has reacted to the dicarboxylic acid fed in. Residence times suitable for the purpose vary from about 2 to 8 hours. depending on the chosen temperatures and the nature of the reactants.

A preferred embodiment ofthe present invention. in which the polyesterit'ication is carried out in three stages. is illustrated in FIG. 1. More particularly. the reacting mixture is passed through the reactors 2, 3, and 4 in succession. the feed taking place through the pipes ll, 13. and 15. respectively. The polyesterification water is eliminated from the individual reactors through the pipes 12, I4. and 16. The reactors 2, 3, and 4 are also fitted with stirrers and means of heat exchange. The polyesteritication product discharged from the reactor 4 is fed through the pipe 17 to the evaporator 5. In said evaporator, which preferably operates by the thin film technique. the residual water and excess alcohol component are eliminated. the operation being carried out at a pressure below atmospheric pressure. preferably from about 2 to 50 mmHg. The evaporator 5 is preferably operated at temperatures not exceeding the polyesteritication temperatures. The polyestcritication product discharged from the evaporator 5 is fed through the pipe 19 to the container 6. into which a monomeric acrylic or vinyl compound may be fed through the pipe 20. The unsaturated polyester rcsin. which contains the monomeric acrylic or vinyl compound, preferably styrene, in a quantity of from about 20 to fill percent by weight, is discharged through the pipe 2].

The unsaturated dicarboxylic acids or their anhydrides used for the purposes of the present invention are those normally used in the art, such as maleic acid and its anhydride. itaconic and fumaric acid. Generally, maleic acid or maleic acid anhydride are used, and a part thereofis replaced by a saturated dicarboxylic acid or its anhydride, such as succinic acid and its anhydride, sebacic acid, phthalic acid and its anhydride, and isophthalic, terephthalic, or adipic acid. Small quantitics of monocarboxylic acids or their anhydrides may also be present in the reaction mixture.

The alcohol components that can be used for the purpose are normally dihydric alcohols, such as 1,2- propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, butylcne glycol, 1,6-hexandeiol, dipropylene glycol, and neopentyl glycol. A part of the dihydric alcohol may be replaced by higher polyhydric alcohols having three, four or five or more hydroxyl groups per molecule; cf. Ullmanns Encyclopadie der technischen Chemie, Third Edition, Vol. 14(1963), p. 90.

The unsaturated polyesters prepared according to the invention may be blended with conventional poly merizable monomeric acrylic or vinyl compounds. Examples of these so-called reactive diluents are given in Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition. Vol. 20 l 1969), pp. 816 to 822 and in Encyclopedia of Polymer Science and Technology, Vol. ll (I969), pp. l5} to I64.

The process of the present invention is particularly useful for the preparation of unsaturated polyesters in which phthalic anhydride, maleic anhydride, and I,'

propylene glycol are polyesterified. These unsaturated polyesters are characterized by especially favourable properties and are particularly suitable for preparing unsaturated polyester resins which contain styrene as monomeric vinyl compound.

This preferred embodiment will be illustrated, again with reference to the attached FlG.

Maleic anhydride and phthalic anhydride are fed to the reactor 1 through the pipe 7 in a molar ratio of from about I12 to 2:l. l,2-Propylene glycol is fed to the reactor through the pipe 9 in such amounts that the molar ratio of the dicarboxylic acid anhydrides to 1,2- propylene glycol is of from about l.5:1 to 1.9:]. The reactor 1 is heated to temperatures of about 100 to IZOC at atmospheric pressure. with a residence time of about 5 to minutes. A product having an acid value of from about 270 to 300 is obtained.

The half-ester obtained in this way is discharged from the reactor 1 through the pipe I], and a further quantity of LZ-propylene glycol is added in such a way as to gi\e a molar ratio of the dicarboxylic acid anhydrides to the I.Z-propylcne glycol of from about 0.80: l to 0.97:]. This mixture is then fed to the reactor 2, which is operated at about 190 to 210C, at pressures of about 3 to 4 atmospheres, and with a residence time of about 20 to 80 minutes. Operating under these conditions, a product having an acid value of about 130 to I41) and a density of about L23 to L at l()()C is fed to the reactor 3 through the pipe 13. The reactor 3 is operated at about 190 to Z l()C. at about L8 to 2.0 atmospheres, and with a residence time of about 20 to 70 minutes, Operating in this way. the product discharged from the reactor 3 has an acid value of about 90 to lUt) and 21 Gardner viscosity at 25C of G-.! when the said viscosity is measured in percent solution in toluene. The product obtained in this way is led through the pipe 15 to the reactor 4, which is operated at atmospheric pressure. This reactor is also operated at temperatures of about l to 2l()C', the residence time being about 30 to 50 minutes. The polycsterification water is eliminated from reactors 2, 3, and 4 through the pipes l2, l4, and 16, respectively.

The product discharged at the base of the reactor 4 is fed through the pipe 17 to a thin film evaporator S, which is operated at temperatures of from about l9() to 220C and at pressures of from about 2 to 3() mmHg. In this way, the residual water and the excess 1,2 propylene glycol, as well as byproducts of the reaction, are eliminated through the pipe 18.

The unsaturated polyester obtained having an acid value of about 40 to 50 and a Gardner viscosity of T-W measured in 70 percent solution in toluene is finally led through the pipe 19 to the container 6, into which styrene is also fed through the pipe 20. The container 6 is operated at about 50 to 60C, and the unsaturated polyester is discharged through the pipe 2].

The process of the present invention is first of all simple and economically convenient, and furthermore, conventional equipment is required. The reactors suitable for the purpose consist of cylindrical steel reactors fitted with stirrers, manometers for the measurement of the pressure, valves for the regulation of the pressure, and pumps for the transport of the fluid.

By operating in the manner described, one avoids any gelation phenomenon in the reacting mass. It is thought that the particularly favourable results obtainable by the process of the present invention are due at least in part to the particular method of carrying out the poly esterification phase. Because of the easy elimination of water, short residence times are possible, and this enables products having low viscosity values and improved colour to be obtained.

Operation in the manner described probably avoids the occurrence of reactions involving the ethylenic double bonds during the polyesterification. Finally, the unsaturated polyesters of the present invention after diluting them with conventional polymerizable monomeric acrylic or vinyl compounds, harden under the influence of conventional polymerization initiators, accelerators and promotors to give products having excellent mechanical and physico-chemical characteristics.

The invention is further illustrated by the following non-limiting examples.

EXAMPLE l With reference to the attached FIG. 1, phthalic anhydride and maleic anhydride are introduced into the reactor through the pipe 7. l,2-Propylene glycol is introduced through the pipe 8. The feeds, which are car ried out continuously, are adjusted to give a molar ratio phthalic anhydridecmaleic anhydride: LIZ-propylene glycol of lzlzlOS. In particular, 60 percent of the l,2- propylene glycol is fed to the reactor 1 through the pipe 9, the remaining part being passed through the pipe 10. In the reactor 1, the formation of the half-ester is carried out at l 10C, at atmospheric pressure, and with a residence time of l5 minutes. The product discharged at the base of the reactor 1, which has an acid value of 290, is mixed with the 1,2-propylene glycol fed through the pipe 10 and introduced into the reactor 2, which is operated at 3.3 atmospheres, at 205C, and with a residence time of 70 minutes. The esterification water is eliminated from the reactor 2 through the pipe 12, and a product with an acid value of I40 and a density of 1.27 measured at 100C is recovered. This product is fed to the reactor 3, which is operated at 205C, at 1.9 atmospheres, and with a residence time of 60 minutes. The polyesterification water is eliminated from the reactor 3 through the pipe 14, and a product having an acid value of 100 and a Gardner viscosity of l, measured at C in 70 percent solution in toluene, is discharged from the reactor. This product is discharged from the reactor 3 and fed through the pipe 15 to the reactor 4, which is operated at normal pressure, at 205C, and with a residence time of minutes, and then to the thin-film evaporator 5. The evaporator is operated at 205C and at 50 mmHg, and a product having an acid value of 50 and a Gardner viscosity of V, measured in the usual manner, is discharged at the base and fed into the container 6 through the pipe [9. Dilution is finally carried out with styrene in the container 6, the quantity of styrene being parts by weight per 100 parts by weight of the unsaturated polyester. The styrene contains p tert.butylhydroquinone as inhibi' tor. lhe unsaturated polyester resin obtained in this way has the characteristics summarized in Table 1. In particular, the viscosity is determined with a Holde- Ubbelohde viscometer at 25C. The gel time is determined at 25C. 0.2 ml ofa (1 percent solution of cobalt octoate in toluene/xylene 1:1 are added to 100 grams of the unsaturated polyester resin. The components are mixed and heated to 25C. The mixture is kept in a thermostated bath and 1.5 ml of a percent solution of methyl ethyl ketone peroxide in dimethylphthalate are added and thoroughly mixed. Gelation has oc curred when the unsaturated polyester resin. on being touched with a glass rod, does no longer stick to the glass rod. The time that has elapsed since the addition of the peroxide is defined as the gel time. The S.P.1. gel time is determined by the S.P.l. method; cf. Kirk- Othmer, Encyclopedia of Chemical 'lcchnology, Second Edition. Vol, 20( 1969), pp. 808 to 809. For determining the storage lit'e the unsaturated polyester resin is subjected to an accelerated test. 50 grams of the polyester resin are filled into a tube which is then closed and heated to C. The fluidity of the polyester resin is observed every 24 hours. When 50 percent of the resin has gelled, the time is taken in days.

The solubility in styrene is determined by adding increasing quantities of styrene to 10 grams of unsaturated polyester, the operation being carried out at 20C.

EXAMPLE 2 The procedure of Example l is followed, phthalic anhydride, maleic anhydride and 1,2-propylene glycol being reacted in a molar ratio of 1:07:18

With reference to FlG. l, 50 percent of the 1,2- propylene glycol is fed into reactor 1, the remainder being fed into reactor 2. With operation as in the first example. a product having an acid value of 136 and a density of 1.25 at 100C is discharged from the reactor 1, a product having an acid value of 95 and a Gardner viscosity of H measured at 25C in percent solution in toluene is discharged from the reactor 3, and finally a product having an acid value of45 and a Gardner viscosity of U measured in the usual manner is discharged from the evaporator S. The unsaturated polyester obtained is diluted with styrene as in Example 1, and the unsaturated polyester resin has the characteristics summarized in Table l.

EXAMPLE 3 The procedure of Example 1 is followed. phthalic anhydride, maleic anhydride, and 1,2-propylene glycol being reacted in a molar ratio of 1:0.5:1.62. 50 percent of the 1,2propylene glycol is introduced into the reactor 1, the remainder being introduced into the reactor 2. With operation as in the first example, a product with an acid value of 270 is discharged from the reactor 1, a product with an acid value of 132 and a density of 1.23 at 100C from the reactor 2, a product with an acid value of and a Gardner viscosity of G, measured at 25C and in 70 percent solution in toluene, from the reactor 3, and finally a product with an acid value of 42 and a Gardner viscosity of T measured in the usual manner, is discharged from the evaporator 5. The unsaturated polyester obtained is diluted with styrene as in Example 1, and the unsaturated polyester resin has the characteristics summarized in Table l.

COMPARATIVE EXAMPLE 1 Phthalic anhydride, maleic anhydride, and propylene glycol are introduced in a molar ratio of 111:2.08 into a flask fitted with a condenser, a stirrer, a thermometer, and a sparge for the introduction of inert gas. The mixture is polymerized at temperatures from 160 to 200C, with introduction of nitrogen and with elimination of the reaction water, until an unsaturated polyester with an acid value of 27.4 is obtained. The product is finally diluted with styrene in a quantity of 35 parts by weight per parts by weight of the unsaturated polyester. The unsaturated polyester resin obtained in this way has the characteristics summarized in Table l.

COMPARATIVE EXAMPLE 2 The procedure of Comparative Example 1 is followed, phthalic anhydride, maleic anhydride, and 1,2- propylene glycol being reacted in a molar ratio of 1:07:18 The unsaturated polyester obtained has an acid value of 26.4. The product is finally diluted with styrene in a quantity of 35 parts by weight per 100 parts by weight of the unsaturated polyester. The unsaturated polyester resin has the characteristics summa rized in Table l.

COMPARATIVE EXAMPLE 3 The procedure of Comparative Example 1 is followed, phthalic anhydride, maleic anhydride, and 1,2- propylene glycol being reacted in a molar ratio of 1:0.5:1.62. The unsaturated polyester obtained has an acid value of 27.2. The product is finally diluted with styrene in a quantity of 35 parts by weight per 100 parts by weight of the unsaturated polyester. The unsatu rated polyester resin has the characteristics summa rized in Table 1.

The unsaturated polyester resins prepared in accordance with Examples 1 to 3 and Comparative Examples 1 to 3 are cured. 0.2m1 of 6 percent solution of cobalt octoate in toluene/xylene 1:1 and 1.5 m1 of a 50 percent solution of methy ethyl kctone peroxide in dirne thylphthalate are added to 100 grams of the unsaturated polyester resin and thoroughly mixed. The mixture is heated to 25C. The following characteristics are determined on the specimens:

A) l'lexurzil strength, kg/cm (ASTM-D 791)) 11) modulus of elasticity in bending.

k /em" [ASTM-D 290) C) impact strength (Charp) 1.

kg cm/cm lASTM-D 256) D) miter absorption of u glass fibre reinforced laminate. "/1 (ASTM D 571)) E) heat distortion temperature,

C (ASTM-D 648) "The laminate is prepared by impregnating a glass fibre mat with the unsaturated polyester rcsin contummg the inltlator. 'l he impregnated mat is enclosed he! een sheets of polyester and excess resin is expressed therefrom until a eight ratio of glass fibre to resin of 3t! 711 is obtained. Curing is efiected for 24 hours at room temperature and one additional hour at 100C The characteristics found for the specimens are shown in Table 11.

the range of from about 0.87:1 to 0.97: 1;

bringing about the polyesterification in a second reaction phase by treating the product obtained in b) in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure, for a total time of from about 2 to 8 hours, and at temperatures of from about 100 to 220C, the temperature between said stages not differing by more than about 10C, the water formed during the polyesterification being eliminated from each of the said stages;

d. evaporating the residual water and the excess of the alcohol component from the polyesterification product obtained in c) with operation at pressures below atmospheric pressure.

2. The process of claim 1, wherein the polyesterification is carried out in 3 to 4 reaction stages, with a pressure that decreases in the various stages from about Remarks "cl lurk-()lhmer. F.l\ \l2l\)pCtilit of Chemical Technology. Second Edition, Vol. H969), pp,

film-HIM H0. 5. S Pl gel time is the time interuil for the tcrnrwrature to change from (15.5 to 88C (151] to 190?) lien the bath temperature is 82C 1 180 F), cf. KirkUthmcr. ih|d.. pp Kl|t to R13. cf Kirk'Uthmcr, ilml p KU'J. l-l(i 5.

TABLE II Characteristics of the cured polyester resins A B C D E Example I 840 41 X 10 3,2 1,06 76 Example 2 590 45 X 10" 2,3 1,12 72 Example 3 750 42 X 1O" 3,6 1,31 61 Comp, Example I 790 41 X 10" 2,9 1,08 74 Comp. Example 2 560 44 X 10 2,1 1.26 68 Comp, Example 3 700 42 X 1O" 3,4 1,28 60 What we claim is:

b. adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in 3 to 4 atmospheres to atmospheric pressure.

3. The process of claim 1, wherein the evaporation in step d) is carried out by a thin-film technique at pressures of from about 2 to mmHg and at temperatures not exceeding the polyesterification temperatures.

4. The process of claim 1, wherein as olefinically unsaturated dicarboxylic acid components maleic acid and its anhydride, itaconic or fumaric acid are used.

5. The process of claim 1, wherein as saturated dicarboxylic acid components succinic acid and its anhydride, sebacic acid, phthalic acid and its anhydride, and isophthalic, terephthalic or adipic acid are used.

6. The process of claim 1, wherein as dihydric alcohol components 1,2-propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, butylene glycol, dipropylene glycol, 1,6-hexanediol or neopentyl glycol are used.

7. The process of claim 1, wherein maleic acid anhydride, phthalic acid anhydride and l ,2-propylene glycol are used.

8. In a process for producing unsaturated polyester mixtures consisting of mixing unsaturated polyesters with at least one polymerizable monomeric acrylic or vinyl compound the improvement which comprises continuously producing said unsaturated polyesters by the steps of:

a. bringing olefinically unsaturated dicarboxylic acids or their anhydrides, if desired together with saturated dicarboxylic acids or their anhydrides (dicarboxylic acid component) and dihydric alcohols, if desired together with higher polyhydric alcohols (alcohol component) into contact in molar ratios of from about 1.5:] to 1.95:1 in a first reaction phase, operating at a temperature of from about 100 to 160C and with residence times of from about to 40 minutes to cause the formation of a corresponding half-ester;

b. adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component is the range of from about 0.87:1 to 0.97:];

ct bringing about the polyesterification in a second reaction phase by the treating the product obtained in b) in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure, for a total time of from about 2 acrylic or vinyl compound is used in a quantity of from about 20 to percent by weight on the unsaturated polyester.

10. The process of claim 9, wherein the monomeric vinyl compound is styrene. 

1. A process for the continuous production of unsaturated polyesters, which comprises the steps of a. bringing olefinically unsaturated dicarboxylic acids or their anhydrides, if desired together with saturated dicarboxylic acids or their anhydrides (dicarboxylic acid component) and dihydric alcohols, if desired together with higher polyhydric alcohols (alcohol component) into contact in molar ratios of from about 1.5:1 to 1.95:1 in a first reaction phase, operating at a temperature of from about 100* to 160*C and with residence times of from about 5 to 40 minutes to cause the formation of a corresponding half-ester; b. adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in the range of from about 0.87:1 to 0.97:1; c. bringing about the polyesterification in a second reaction phase by treating the product obtained in b) in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure, for a total time of from about 2 to 8 hours, and at temperatures of from about 100* to 220*C, the temperature between said stages not differing by more than about 10*C, the water formed during the polyesterification being eliminated from each of the said stages; d. evaporating the residual water and the excess of the alcohol component from the polyesterification product obtained in c) with operation at pressures below atmospheric pressure.
 2. The process of claim 1, wherein the polyesterification is carried out in 3 to 4 reaction stages, with a pressure that decreases in the various stages from about 3 to 4 atmospheres to atmospheric pressure.
 3. The process of claim 1, wherein the evaporation in step d) is carried out by a thin-film technique at pressures of from about 2 to 50 mmHg and at temperatures not exceeding the polyesterification temperatures.
 4. The process of claim 1, wherein as olefinically unsaturated dicarboxylic acid components maleic acid and its anhydride, itaconic or fumaric acid are used.
 5. The process of claim 1, wherein as saturated dicarboxylic acid components succinic acid and its anhydride, sebacic acid, phthalic acid and its anhydride, and isophthalic, terephthalic or adipic acid are used.
 6. The pRocess of claim 1, wherein as dihydric alcohol components 1,2-propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, butylene glycol, dipropylene glycol, 1,6-hexanediol or neopentyl glycol are used.
 7. The process of claim 1, wherein maleic acid anhydride, phthalic acid anhydride and 1,2-propylene glycol are used.
 8. IN A PROCESS FOR PRODUCING UNSATURATED POLYESTER MIXTURES CONSISTING OF MIXING UNSATURATED POLYESTERS WITH AT LEAST ON POLYMERIZABLE MONOMERIC ACRYLIC OR VINYL COMPOUND THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY PRODUCING SAID UNSATURATED POLYESTERS BY THE STEPS OF: A. BRINGING OLEFINICALLY UNSATURATED DICARBOXYLIC ACIDS OR THEIR ANHYDRIDES, IF DESIRED TOGETHER WITH SATURATED DICARBOXYLIC ACIDS OR THEIR ANHYDRIDES (DICARBOXYLIC ACID COMPONENT) AND DIHYDRIC ALCOHOLS, IF DESIRED TOGETHER WITH HIGHER POLYHYDRIC ALCOHOLS (ALCOHOL COMPONENT) INTO CONTACT IN MOLAR RATIOS OF FROM ABOUT 1.5:1 TO 1.95:1 IN A FIRST PHASE, OPERATING AT A TEMPERATURE OF FROM ABOUT 100* TO 160*C AND WITH RESIDENCE TIMES OF FROM ABOUT 5 TO 40 MINUTES TO CAUSE THE FROMATION OF A CORESPONDING HALF-ESTER, B. ADDING TO THE HALF-ESTER FORMED A FURTHER QUANTITY OF THE ALCOHOL COMPONENT IN SUCH A WAY AS TO GIVE A MOLAR RATIO OF THE DICARBOXYLIC ACID COMPONENT TO A TOTAL AMOUNT OF THE ALCOHOL COMPONENT IS THE RANGE OF FROM ABOUT 0.87:1 TO 0.97:1, C. BRINGING ABOUT THE POLYESTERIFICATION IN A SECOND REACTION PHASE BY THE TREATING PRODUCT OBTAIN IN B) IN AT LEAST TWO SEPARATE AND SUCCESSIVE STAGES, WHICH ARE OPERATED AT DECREASING PRESSURE VALUES IN THE RANGE OF FROM ABOUT 5 ATMOSPHERES TO ATMOSPHERIC PRESSURE, FOR A TOTAL TIME OF FROM ABOUT 2 TO 8 HOURS, AND AT A TEMPERATURES OF FROM ABOUT 100* TO 220*C, THE TEMPERATURE BETWEEN SAID STAGES NOT DIFFERING BY MORE THAN ABOUT 10*C, THE WATER FORMED DURING THE POLYESTERIFICATION BEING ELIMINATED FROM EACH OF THE SAID STAGES, D. EVAPORATING THE RESIDUAL WATER AND THE EXCESS OF THE ALCOHOL COMPONENT FROM THE POLYESTERIFICATION PRODUCT OBTAINED IN C) WITH OPERATION AT PRESSURES BELOW ATMOSPHERIC PRESSURE.
 9. The process of claim 8, wherein the monomeric acrylic or vinyl compound is used in a quantity of from about 20 to 60 percent by weight on the unsaturated polyester.
 10. The process of claim 9, wherein the monomeric vinyl compound is styrene. 